With the increasing popularity of "fast food" establishments where food is precooked for later sale, there is a demand for food holding devices to maintain food at substantially uniform temperatures for extended periods of time while preserving the taste and moisture content of the food.
Storage of food for such purposes is difficult in many instances because of heat loss, bacterial growth and moisture loss experienced by the food in storage. Specifically, air circulation and improper storage temperature promotes bacterial growth, excessive loss of moisture and excessive shrinkage so that the food deteriorates in many instances after only a short period of time and loses its tenderness, appetizing taste and appearance.
Various prior art devices and methods are known to store food, for example, as shown in U.S. Pat. No. 4,038,968--Rovell and U.S. Pat. No. 3,955,007--Roderick, where means are provided for humidification and circulation of warm moist air around the food to maintain the food at a uniform temperature while preserving the moisture content therein but such prior art leaves several problems unresolved.
More particularly, U.S. Pat. No. 3,955,007--Roderick utilizes a moisture container assembly mounted in a heat holding compartment located above a gas burner assembly. The amount of moisture circulating in the air in the heat holding compartment bears no relationship to the temperature of the air so the moisture content is subject to change with the rate of heat supplied to the humidifier.
In most prior art arrangements where an attempt is made to maintain temperature of the product while maintaining moisture content, a source of moisture is located in the cabinet, but no attempt is made to interrelate wet bulb and dry bulb temperatures to maintain a desired rate of moisture evaporation to control food shrinkage or food crispness each being important to different foods.
In the storage of some foods, such as fried chicken or fish, where a crust is provided, it is particularly desirable to maintain the crispness of the crust while minimizing moisture loss from the underlying meat. Excessive moisture loss in such instances results in unwanted shrinkage and loss of tenderness and texture of the meat.
Accordingly, prior art devices which provide only saturated air to the storage compartment do not recognize the dynamics of food storage and can lead to situations where breading crust or other materials on the surface of the food become soggy so the food loses its appeal even though the underlying meat may be drying out.
Moreover, a second and equally important problem is caused by bacterial growth in the food. Despite the fact that prior art devices provide means for circulating warm moist air and reduce the rate of moisture loss from food, bacterial growth, if not controlled, simultaneously causes the food to deteriorate so that the food in the warming compartment deteriorates at an accelerated rate.
Another requirement exists in the case of some foods where quality is adversely affected by shrinkage from moisture loss. Typically these foods may be no longer palatable where the moisture loss has reached 5%. The prior art did not provide control of moisture loss and therefore provided no means to effectively control holding time allowable yet not exceed critical shrinkage values.
No previous art is known which teaches or discloses any method providing means to control the evaporation rate from stored food to maintain it at a selected level of crispness while controlling the storage temperature so the food will be maintained relatively free of bacterial growth to extend its storage life and/or provide improved quality of the food as dispensed.
Most present commercial devices concede the importance of increasing the magnitude of the wet bulb temperature by providing a water pan or tray within the compartment to add moisture to the air. None, however, control the wet bulb temperature and dry bulb temperature to preserve a controlled rate of evaporation while preserving the crispness of the crust. Further, air leakage from the cabinet, and frequent door openings, reduce the wet bulb temperature to levels that allow the product to be evaporatively cooled to temperatures well below the critical temperature permitting bacterial growth. In this regard it has been found that in many instances the use of blowers in food holding cabinets can be disadvantageous because of the low pressure at the center of the air moving device which can draw in ambient air and because of the higher pressures resulting from the blower which can cause conditioned air to leak out of the cabinet.